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Tanker Shipping & Trade

Tanker Shipping & Trade

Ecological developments in green tanker technology

Tue 20 Feb 2018 by Brian Warshaw

Ecological developments in green tanker technology
The new shuttle tanker concept brings economic and environmental benefits to owners (credit: Wärtsilä)

In December it was announced that Teekay Tankers had placed a contract with the Samsung Heavy Industries (SHI) yard in South Korea for four new shuttle tankers designed to provide a higher level of ecological and economic operation

Shuttle tankers operate in a different way to seagoing tankers. They load crude oil from offshore platforms working under dynamic positioning conditions, transport oil relatively short distances to land-based terminals, discharge the cargo and return to the platform under ballast. Each of these operations has its own requirements, resulting in the equipment installed on board not being used efficiently in the various operational functions.

Finland’s Wärtsilä Corp will supply key parts of the Teekay shuttle tanker project. Power systems will operate on a combination of liquefied natural gas (LNG), as a primary fuel, and volatile organic compounds (VOC), as a secondary fuel. The Wärtsilä VOC recovery plant uses compression and cooling phases to liquefy the heavier hydrocarbons to liquid VOC (LVOC) that is stored in a tank on the deck of the vessel. The LNG and LVOC will be used in combination as the main power source for the engines. Methane gas emerging from the crude oil cargo during loading or transit, referred to as surplus VOC, is burnt in a gas turbine for electricity generation.  

Compared with the current standard of shuttle tankers, the new design will improve fuel economy by 22%. The use of LVOC as a fuel results in reduced bunkering needs. The elimination of VOC emissions to the atmosphere will eliminate 84% of NOx from the engine exhaust, practically eliminate SOx emissions, and reduce particles to less than 4%. For general shipping, including tankers, Wärtsilä has a range of dual-fuel (DF) engines designed to seamlessly operate using natural gas, marine diesel oil, heavy fuel oil and biofuels, thereby providing maximum flexibility in fuel choice based on location and bunker prices. Ecologically, a medium-speed DF engine running on natural gas reduces CO2 emissions by approximately 30%, NOx by 85%, while SOx and particulates are almost entirely eliminated compared with operating in gasoil mode.

By the expedient of changing from gasoil to LNG, operating costs will be reduced and the problems of noxious atmospheric emissions will be eliminated in a way that cannot be falsified.

Rewards for innovative shipowners

The Teekay shuttle tankers are evidence of owners’ and operators’ continuing interest in vessels that demonstrate innovative environmental developments. Partly this is the pull of regulation, partly the economic gains that follow, and partly a growing realisation of environmental needs.

At October 2017’s Fathom Fleet Transformation Event in London, IACS chairman Knut Ørbeck-Nilssen said that an effective regulation should reward early adopters. “At the moment, it can be argued that those who adopt last get the best financial return. IACS is working to adapt regulations to new needs and remove regulatory barriers that are hindering new technical advances. Also, IACS aims to ensure that an appropriate balance is struck between environmental and safety regulation. It has to be avoided that regulations are developed in isolation of one another,” he stated. 

Regulation through IMO was the precursor to reduction in exhaust emissions, and it is encouraging to observe that Intertanko, the main shipowners’ organisation, submitted a proposal to the IMO Sub-Committee on Pollution Prevention and Response to ban the carriage of non-compliant fuels for propulsion unless an approved alternative compliance method is used.

Free flow of ballast water through the vessel

The second major environmental advance driven by regulations is the IMO Ballast Water Management (BWM) Convention, which for new ships entered into force on 8 September 2017. Existing ships must comply at the first International Oil Pollution Prevention Certificate inspection after 8 September 2019.

The regulations that seek to control the spread of invasive aquatic species through ships’ ballast water require seagoing vessels to manage their ballast by exchanging ballast water throughout the voyage, or by treating it using an approved ballast water management system. The BWM Convention also allows for undefined ‘Alternatives,’ whereby a ship may be designed so that it does not carry ballast water beyond a bioregion.

IMO’s Marine Environment Protection Committee (MEPC) guidelines to address the issue were adopted in 1991. Thirteen years later, Saudi Arabia put forward a paper relating to a patent held by Vela International Marine Limited1 as a particular solution for VLCCs. Vela argued that the current technologies were too expensive, would cost in excess of US$1M to retrofit on a VLCC-sized ship, have an OPEX of approximately US$100,000 per passage and would add a week to the discharge time of every VLCC.

In comparison, Vela asserted that its own automatic ballast flow (AUBAFLOW2) technology was an alternative concept that simply attached to the existing ballast system. Its cost would be approximately US$500,000 to retrofit in a VLCC, with minimal extra costs to train the crew members to operate, maintain and achieve the control requirements demanded by the IMO’s BWM regulations.

AUBAFLOW enables water to flow through the double bottom of the ship as it moves through the water. The technology effectively ‘ballasts’ down the vessel to the Marpol draft by reducing buoyancy rather than adding weight into the ballast tanks.

With the bottom of the ship open, the seawater will rise inside the ballast tanks to a height equal to the ship’s draught. When the ship moves forward, the pressure created by the movement causes the seawater to flow into the wing walls and flow through sluice gates on deck or at the sheer strake before being returned to the sea.

On arrival at the port berth, the AUBAFLOW system is closed and the ship reverts to its normal mode in order to deballast. The ballast water on the ship will have been collected from a maximum distance of 800 km, thereby meeting the relevant regulations. With a 600 mm AUBAFLOW entry, a ship making 14 knots will fully exchange three volumes every 800 km. This will mean that on crossing most bioregions, all ballast will have been completely exchanged before the ship crosses into an adjacent bioregion, maintaining compliance with the regulations.

At its meeting held in May 2007, the MEPC received a presentation by Saudi Arabia and India proposing the AUBAFLOW design as an alternative ballast water management system. Nothing further has been published about this project, but it remains a viable proposal, especially with container ships now frequently being built to exceed 20,000 TEU, for Bahri Oil or another company to take forward.

At the end of last year, a team of students from the University of Michigan’s school of Naval Architecture & Marine Engineering won first prize at the Society for Naval Architects and Marine Engineers Annual Meeting with its design for a ballast-free LNG carrier vessel.

In a concept similar to the one used by AUBAFLOW, the students’ design, based on an advanced double-hull structure, enables a constant flow of water to pass through the bottom of the ship. The student team claims it would reduce the environmental impact of transoceanic trade, while improving the overall efficiency of the vessel. But like AUBAFLOW, and Nikša Fafandjel3, the team has yet to prove its claims.

1 In June 2012 Saudi Aramco agreed to sell Vela to Saudi National Shipping Company, which merged with Bahri Oil in 2014.

2 Scott, Thomas J., “AUBAFLOW – Automatic Ballast Flow,” Saudi Aramco Journal of Technology, Summer 2005, pp. 2-8.

3 Fafandjel N., et al, An Approach to Ship Water Ballast Management by Continuous Flow-through Method, 2011,

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